1. Field of the Invention
The present invention relates to a pump apparatus such as a fuel pump for forcedly delivering fuel from a tank into an internal combustion engine mounted on a vehicle.
2. Description of the Prior Art
In the field of pumps of the class specified above, various types of pumps have been used, such as displacement type pump (for example, roller pump), centrifugal type pump (for example, axial flow pump), and regenerative pump of open vane type. The displacement type pumps, such as roller pump, are operative to produce a high pressure of about 2 to 3 Kg/cm.sup.2 and provide a high efficiency. The pumps of this type, however, must be manufactured with a high precision and, hence, are generally expensive. The pumps of this type, moreover, produce noise and vibration and, in addition, pulsated discharge pressure. With the pumps of centrifugal type, it is difficult to obtain a high discharge pressure of 2 to 3 Kg/cm.sup.2. The regenerative pump of open vane type also are not capable of producing a high discharge pressure of 2 to 3 Kg/cm.sup.2, and can operate only at a low efficiency. In addition, this "open vane type pump" often faces restrictions of installation space. Due to this restriction, it is not allowed to provide the discharge port in the peripheral wall of the pump housing. Consequently, the discharge port has to be provided in one end wall of the pump housing. As a result, a thrust is imparted to the impeller for a reason which will be detailed later with reference to the drawings, so that the impeller is undesirably biased to contact the inner surface of the pump housing. In consequence, the efficiency of the pump is lowered and the life of the same is shortened unfavourably. The term "regenerative pump of open vane type" means a regenerative pump in which the bottom face of each of vane grooves formed in one of end faces of a disc-like impeller intersects with the bottom face of an adjacent vane groove formed in the other end face of the impeller. In contrast to this, by the term "regenerative pump of closed vane type" to be used in hereinafter it is intended to mean a regenerative pump in which the bottom face of each of vane grooves formed in one of the end faces of a disc-like impeller does not intersect with the bottom face of an adjacent vane groove formed in the other end face of the impeller.